Ink supply mechanism and image forming device

Abstract

To suppress ink having air dissolved therein and thickened and stuck ink from being supplied to a recording head to suppress the recording head from being poorly operated, and also suppress evaporated and thickened ink from having an influence on sensing of a level sensor.SOLUTION: An ink supply mechanism 20 provided in a printer 1 is provided with: an ink container 14 that stores ink; a sub tank 22 that stores ink supplied from the ink container 14; a main flow path 24 extending downward form the sub tank 22, through which ink is flown between the ink container 14 and the sub stank 22; and a branched flow path 25, branched from the middle of the main flow path 24, which receives hydraulic head pressure of the ink stored in the sub stank 22 in order to supply ink towards the recording head 13.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an ink supply mechanism for supplying ink to a recording head and an image forming apparatus including the ink supply mechanism. [Background technology]

[0002] Conventionally, an inkjet image forming apparatus includes a recording head that ejects ink onto a recording medium such as paper, an ink container that stores ink, and a sub-tank that stores the ink supplied from the ink container, and supplies ink to the recording head by utilizing the head pressure between the sub-tank and the recording head. In the image forming apparatus, the ink liquid surface in the sub-tank is in contact with air, and it is necessary to prevent air from dissolving in the ink.

[0003] For example, in Patent Document 1, a supply liquid tank unit provided in an inkjet recording device includes a supply liquid tank that stores ink to be supplied to a recording head that ejects ink onto a recording medium, and a detection sensor that detects the ink level in the supply liquid tank. The supply liquid tank is provided with an internal space having a storage chamber that stores ink, and an air opening port that equalizes the internal pressure of the internal space with atmospheric pressure. The detection sensor includes a float that moves up and down depending on the amount of ink in the storage chamber, and a sensor body that detects the ink level as the float moves up and down. The inner surface of the storage chamber is disposed close to and along the outer circumferential surface of the float. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-025741 A Summary of the Invention [Problem to be solved by the invention]

[0005] In conventional image forming devices such as that described in Patent Document 1, the speed at which air dissolves in the ink can be slowed down by placing the float close to the wall of the subtank, but the ink with dissolved air diffuses due to the Brownian motion of the liquid. As a result, the ink with dissolved air is supplied to the recording head, which may cause a malfunction of the recording head that prevents ink from being ejected.

[0006] In addition, in a conventional image forming apparatus such as that in Patent Document 1, the detection sensor is composed of a float and a sensor body, and the inner surface of the storage chamber, which is a sub-tank, is arranged close to the outer circumferential surface of the float, and the sensor body is inserted into the center of the float. However, if the ink in the sub-tank evaporates or thickens due to contact with the float, the ink may adhere between the float and the sensor body, or between the inner surface of the storage chamber and the outer circumferential surface of the float. As a result, the float may not operate properly relative to the sensor body or the float may not operate properly relative to the storage chamber, resulting in detection failure. In addition, if the thickened or solidified ink gets into the flow path from the sub-tank to the recording head, the nozzle of the recording head may be clogged, causing the recording head to malfunction.

[0007] Therefore, in consideration of the above circumstances, the present invention aims to prevent malfunction of the print head by suppressing the supply of ink containing dissolved air or thickened / solidified ink to the print head, while also suppressing the effect on the detection of the level sensor caused by evaporated / thickened ink. [Means for solving the problem]

[0008] The ink supply mechanism of the present invention is characterized by comprising an ink container for containing ink, a subtank for storing the ink supplied from the ink container, a main flow path extending downward from the subtank and circulating the ink between the ink container and the subtank, and a branch flow path branching off midway from the main flow path and receiving a hydraulic head pressure of the ink stored in the subtank in order to supply the ink toward a recording head.

[0009] The image forming apparatus of the present invention is characterized by including the ink supply mechanism described above. Effect of the Invention

[0010] According to the present invention, it is possible to prevent ink containing dissolved air or ink that has thickened or solidified from being supplied to the recording head, thereby preventing malfunction of the recording head and suppressing the effect on the detection of the level sensor caused by evaporated or thickened ink. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional view illustrating an example of a printer according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram illustrating an example of an ink supply mechanism of a printer according to an embodiment of the present invention. [Diagram 3] FIG. 1 is a cross-sectional view illustrating an example of a subtank of a printer according to an embodiment of the present invention. [Figure 4] FIG. 11 is a block diagram illustrating an outline of a first modified example of an ink supply mechanism of a printer according to an embodiment of the present invention. [Diagram 5] FIG. 11 is a block diagram illustrating an outline of a second modified example of an ink supply mechanism of a printer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] First, the overall configuration of the printer 1 as an inkjet image forming apparatus will be described with reference to Fig. 1. For ease of explanation, the front side of the paper in Fig. 1 is the front side of the printer 1. Arrows L, R, U, and Lo appropriately added to each figure indicate the left side, right side, upper side, and lower side of the printer 1, respectively.

[0013] As shown in Fig. 1, the printer 1 includes a box-shaped printer main body 2. A paper feed cassette 3 for storing paper is housed in the lower part of the printer main body 2 and can be removed.

[0014] A paper transport path 4 is provided on the right side of the printer body 2, and a paper transport unit 5 that can be raised and lowered is provided above the paper feed cassette 3 in the center of the printer body 2. The transport path 4 runs from the paper feed cassette 3 to the paper transport unit 5, and along the paper transport direction of the transport path 4, a paper feed roller, a transport roller, and a registration roller are provided in this order from upstream.

[0015] The paper transport unit 5 includes a transport frame 6 and an endless transport belt 7 (transport member). A drive roller, a driven roller, and a tension roller are rotatably provided on the transport frame 6, and the transport belt 7 is replaceably attached to the transport frame 6 and wound around the drive roller, the driven roller, and the tension roller. The transport belt 7 is controlled by the control unit 16 described below so as to rotate, for example, counterclockwise when viewed from the front, in response to the rotation of the drive roller, and transport paper on the transport belt 7 from right to left.

[0016] The paper transport unit 5 also has an elevation mechanism (not shown) capable of raising and lowering the transport frame 6 and the transport belt 7 in the vertical direction, and moves the transport frame 6 and the transport belt 7 to a printing position close to the recording head 13 described below during printing operation, and moves them to a retracted position away from the recording head 13 during non-printing operation. The paper transport unit 5 also has an air intake section 5a on the inside of the transport belt 7. The transport belt 7 has many air intake holes, and the air intake section 5a draws air from above the transport belt 7 to the inside through the air intake holes.

[0017] On the left side of the printer body 2, a paper transport section 8, a drying device 9, and discharge rollers 10 are provided to the left of the paper transport unit 5 at the printing position in order to discharge paper after printing. On the left side of the printer body 2, a discharge outlet 11 is formed near the discharge rollers 10, and below the discharge outlet 11, a paper output tray 12 is provided protruding to the left.

[0018] Additionally, within the printer body 2, there are provided four recording heads 13 (13K, 13C, 13M, 13Y) that eject ink corresponding to the four colors of ink, black, cyan, magenta, and yellow, respectively, and four ink containers 14 (14K, 14C, 14M, 14Y) that store the ink. Each recording head 13 is connected to each ink container 14 via an ink supply mechanism 20 that has a suction pump 21 and a sub-tank 22. Note that in FIG. 1, the ink supply mechanism 20 corresponding to black ink is illustrated, and the ink supply mechanism 20 corresponding to cyan, magenta, and yellow ink is omitted.

[0019] A plurality of nozzles 13a that eject ink droplets are formed on the undersides of the recording heads 13K, 13C, 13M, and 13Y. The recording heads 13K, 13C, 13M, and 13Y are arranged side by side above the paper transport unit 5 in the center of the printer body 2, and are arranged, for example, in order from the upstream side (right side) in the paper transport direction. The recording heads 13K, 13C, 13M, and 13Y face the upper surface of the transport belt 7 of the paper transport unit 5 during printing operation, and eject black, cyan, magenta, and yellow ink, respectively, onto the paper on the transport belt 7.

[0020] The ink containers 14K, 14C, 14M, and 14Y are arranged side by side in the lower left corner of the printer main body 2, for example, arranged in order from the bottom up. The ink containers 14K, 14C, 14M, and 14Y are, for example, removably stored in respective container storage units (not shown) provided in the lower left corner of the printer main body 2. The ink containers 14K, 14C, 14M, and 14Y store black, cyan, magenta, and yellow ink, respectively.

[0021] Also provided within the printer main body 2 is a control unit 16 that controls each part of the printer 1. The control unit 16 is a computer consisting of a CPU and the like, and controls each part of the printer 1 connected to the control unit 16 by executing calculations based on control programs and control data stored in a storage unit (not shown) consisting of a ROM, RAM, HDD, etc.

[0022] Next, the ink supply mechanism 20 will be described in detail.

[0023] The ink supply mechanism 20 is a mechanism that supplies ink from each ink container 14 (14K, 14C, 14M, 14Y) to each recording head 13 (13K, 13C, 13M, 13Y). In this embodiment, as shown in FIG. 2, the ink supply mechanism 20 includes, in addition to the recording head 13 and the ink container 14, a suction pump 21, a subtank 22, a supply pump 23, a main flow path 24, a branch flow path 25, a flow path opening / closing unit 26, a restricting member 27, and a head filter 28. The ink supply mechanism 20 is configured to supply ink toward the recording head 13 by utilizing the head pressure of the ink stored in the subtank 22.

[0024] The ink container 14 is connected to a main flow path 24 extending downward from the subtank 22, and ink can flow between the ink container 14 and the subtank 22 via the main flow path 24. Between the ink container 14 and the subtank 22, preferably between the suction pump 21 and the subtank 22, a branch flow path 25 branches off from the middle of the main flow path 24, and ink branched from the main flow path 24 can flow via the branch flow path 25. The branch flow path 25 receives the head pressure of the ink stored in the subtank 22 in order to supply ink to the recording head 13.

[0025] The suction pump 21 is composed of a diaphragm pump or the like, and is controlled by the control unit 16 to supply ink from the ink container 14 through the main flow path 24. The suction pump 21 is provided in the main flow path 24 between the ink container 14 and the subtank 22 (preferably between the ink container 14 and the branch flow path 25), and sucks ink from the ink container 14 and supplies it to the main flow path 24.

[0026] The subtank 22 stores the ink supplied from the ink container 14, and the main flow path 24 is connected to a lower portion (preferably the bottom surface) of the subtank 22. As shown in Fig. 3, the subtank 22 includes a tank body 36 and a level sensor 37. The level sensor 37 is configured, for example, by a movable sensor including a float 38, a movable portion 39, and a float detection portion 40.

[0027] The tank body 36 is a housing that stores ink, and the main flow path 24 is connected to a lower portion (preferably the lower surface) of the tank body 36. The inside of the tank body 36 and the main flow path 24 are in communication, and ink supplied from the main flow path 24 is stored inside the tank body 36. In the tank body 36, an upper limit storage amount of ink, i.e., an upper limit height of the ink liquid level S, is set, and in the subtank 22, the storage amount of ink (liquid level height) is controlled so that it is less than the upper limit storage amount (upper limit height).

[0028] The float 38 is supported by a movable part 39 on the upper inside side of the tank body 36 so as to be movable up and down, and floats on the liquid level S of the ink stored in the tank body 36 at a position separated from the inner wall surface of the tank body 36 (towards the center of the tank body 36). For example, the float 38 is formed in an elongated shape, and is disposed so that its base end is supported by the movable part 39 and its tip is floated on the ink liquid level S. In other words, only a part of the tip of the float 38 comes into contact with the ink liquid level S.

[0029] The movable part 39 is provided on the upper inside side of the tank body 36, above the ink level S so as not to come into contact with the ink stored in the tank body 36, specifically, above an upper limit height set for the tank body 36. The movable part 39 may be provided on the ceiling surface of the tank body 36, or may be provided on the inner wall surface of the tank body 36. The movable part 39 rotatably supports the base end of the elongated float 38, thereby enabling the float 38 to rotate up and down with the movable part 39 as a fulcrum.

[0030] The float detection unit 40 detects the float 38, which moves up and down, to detect the level of the liquid surface S of the ink stored in the subtank 22. For example, a detectable part such as a magnet is provided at the tip of the float 38, and the float detection unit 40, which is provided on the side (e.g., the inner wall surface) of the tank body 36, detects the detectable part of the float 38, so that the level sensor 37 detects the level of the ink stored in the tank body 36.

[0031] The subtank 22 is controlled by the control unit 16, and the amount of ink stored, i.e., the level (height) of the ink surface S is controlled so that the head difference with the recording head 13 becomes a predetermined set value based on the level of the ink surface S detected by the float detection unit 40. The upper limit height of the tank body 36 is set above the ink surface height that realizes the head difference of the predetermined set value, and the tank body 36, float 38 and movable part 39 are preferably designed so that the float 38, when moved to the upper limit height, does not come into contact with the ceiling surface of the tank body 36.

[0032] The supply pump 23 is composed of a syringe pump or the like, and is controlled by the control unit 16 to fill a predetermined amount of ink from a main flow path 24 between the ink container 14 and the subtank 22 and supply it to the recording head 13. A branch flow path 25 is connected to the supply pump 23, and further connected to a filling flow path 29 for filling the ink from the main flow path 24 and a supply flow path 30 for supplying ink to the recording head 13. In addition, a circulation flow path 31 for circulating the ink back to the supply source is connected to the recording head 13, and the circulation flow path 31 is connected to the filling flow path 29 or the main flow path 24.

[0033] The flow path opening / closing unit 26 includes a first opening / closing member 32 that opens and closes the branch flow path 25, a second opening / closing member 33 that opens and closes the supply flow path 30, a third opening / closing member 34 that opens and closes the filling flow path 29, and a fourth opening / closing member 35 that opens and closes the circulation flow path 31. The first opening / closing member 32, the second opening / closing member 33, the third opening / closing member 34, and the fourth opening / closing member 35 are each controlled by the control unit 16 to open or close.

[0034] The limiting member 27 is configured of a porous member, a filter, or the like, and limits the exchange of ink without changing the hydraulic head pressure between the subtank 22 and the branch flow channel 25. The limiting member 27 may be disposed, for example, as shown in Fig. 3, inside the tank body 36 of the subtank 22, facing the bottom surface of the tank body 36 and the ink liquid level S in the vertical direction. Alternatively, the limiting member 27 may be disposed midway in the main flow channel 24 between the subtank 22 and the branch flow channel 25 facing the ink flow direction in the main flow channel 24, or may be attached to the bottom surface of the subtank 22 to which the main flow channel 24 is connected.

[0035] The head filter 28 is provided in the supply flow path 30 between the supply pump 23 and the recording head 13, immediately before the recording head 13, and serves to remove foreign matter from the ink supplied to the recording head 13 via the supply flow path 30.

[0036] In the above embodiment, an example has been described in which the level sensor 37 for detecting the level of ink stored in the tank body 36 in the ink supply mechanism 20 is configured as a movable sensor including the float 38, the movable portion 39, and the float detection portion 40, but the present invention is not limited to this example. In another example, the level sensor 37 may be configured as a fixed sensor including a capacitance sensor, a photointerrupter, or an electrode-type level sensor. In this case, the level sensor 37 is provided above the upper limit height set for the tank body 36.

[0037] Next, an example of the operation of the ink supply mechanism 20 of this embodiment will be described.

[0038] In the ink supply mechanism 20, under normal conditions, the first opening / closing member 32, the second opening / closing member 33, the third opening / closing member 34, and the fourth opening / closing member 35 are all open in the flow path opening / closing section 26. This allows the head pressure of the ink stored in the subtank 22 to act on the recording head 13 via the main flow path 24, the branch flow paths 25, and the supply flow path 30, and the ink filled in the supply pump 23 can be appropriately supplied to the recording head 13.

[0039] During ink filling, the ink supply mechanism 20 opens the third opening / closing member 34, while closing the first opening / closing member 32, the second opening / closing member 33, and the fourth opening / closing member 35. This allows ink to be filled into the supply pump 23 from the main flow path 24 between the suction pump 21 and the subtank 22 via the filling flow path 29.

[0040] During circulation, the ink supply mechanism 20 opens the second opening / closing member 33 and the fourth opening / closing member 35, while closing the first opening / closing member 32 and the third opening / closing member 34. This allows ink to circulate from the recording head 13 through the circulation flow path 31 to the main flow path 24 between the suction pump 21 and the subtank 22.

[0041] During air removal, the ink supply mechanism 20 opens the first opening / closing member 32, while closing the second opening / closing member 33, the third opening / closing member 34, and the fourth opening / closing member 35. This makes it possible to remove unnecessary air from the main flow path 24, the branch flow paths 25, and the supply pump 23.

[0042] As described above, in this embodiment, the ink supply mechanism 20 provided in the printer 1 comprises an ink container 14 that contains ink, a subtank 22 that stores ink supplied from the ink container 14, a main flow path 24 that extends downward from the subtank 22 and allows ink to circulate between the ink container 14 and the subtank 22, and a branch flow path 25 that branches off midway from the main flow path 24 and receives the head pressure of the ink stored in the subtank 22 in order to supply ink to the recording head 13.

[0043] As a result, even if air is dissolved in the ink near the liquid level S of the ink stored in the subtank 22, or if the ink evaporates, thickens, and solidifies, it is possible to prevent the ink with dissolved air or the thickened and solidified ink from flowing through the flow path that supplies the ink to the recording head 13. This makes it possible to prevent malfunctions of the recording head 13, such as ink not being ejected due to ink with dissolved air. It is also possible to prevent malfunctions of the recording head 13, such as clogging of the nozzles 13a of the recording head 13, due to thickened and solidified ink.

[0044] Furthermore, in this embodiment, the ink supply mechanism 20 is equipped with a level sensor 37 that detects the level of the liquid surface S of the ink stored in the subtank 22, and the level sensor 37 is composed of a movable sensor having a float 38 spaced apart from the inner wall surface of the subtank 22 and floating on the liquid surface S, and a movable part 39 that is provided in a position that does not come into contact with the ink and moves the float 38, or a fixed sensor consisting of a capacitance sensor, a photointerrupter, or an electrode-type level sensor that is provided in a position that does not come into contact with the ink.

[0045] As a result, even if ink evaporates, thickens, and solidifies near the liquid level S of the ink stored in the subtank 22, the thickened and solidified ink does not affect the movement of the float 38 relative to the inner wall surface of the subtank 22, and does not affect the movement of the float 38 by the movable part 39, thereby suppressing the effect on detection by the movable sensor level sensor 37. Also, since the thickened and solidified ink does not come into contact with a fixed sensor consisting of a capacitance sensor, a photointerrupter, or an electrode-type level sensor, the effect on detection by the fixed sensor level sensor 37 can be suppressed.

[0046] In addition, in this embodiment, the ink supply mechanism 20 includes a suction pump 21 that supplies ink from the ink container 14 through the main flow path 24, and the branch flow path 25 is disposed between the sub-tank 22 and the suction pump 21.

[0047] This makes it possible, with a simpler configuration, to supply the ink stored in the subtank 22 to the recording head 13 via the branch flow path 25 without changing the head pressure of the ink, and also makes it possible to prevent ink containing dissolved air or ink that has become viscous or has solidified from circulating through the branch flow path 25.

[0048] In addition, in this embodiment, the ink supply mechanism 20 includes a restricting member 27 that restricts the exchange of ink between the subtank 22 and the branch flow path 25 without changing the head pressure.

[0049] As a result, even if air is dissolved in the ink near the liquid level S of the ink stored in the subtank 22, or if the ink evaporates, thickens, and solidifies, it is possible to further prevent the ink with dissolved air or the thickened and solidified ink from flowing through the flow path that supplies ink to the recording head 13.

[0050] In the above embodiment, the ink supply mechanism 20 includes both the suction pump 21 that sucks ink from the ink container 14 and the supply pump 23 that supplies the filled ink to the recording head 13, but the present invention is not limited to this example. In the present invention, the ink supply mechanism 20 only needs to have a configuration in which the branch flow path 25 branches off from the main flow path 24 between the ink container 14 and the subtank 22 and receives the head pressure of the ink stored in the subtank 22 in order to supply ink to the recording head 13, and other flow paths and pumps can be variously combined.

[0051] For example, as shown in Fig. 4, in a first modified example, the ink supply mechanism 20 may be configured to include only a supply pump 50 that supplies filled ink to the recording head 13, without including a suction pump 21 that sucks ink from the ink container 14. In the first modified example, the supply pump 50, such as a syringe pump, is provided in the middle of the main flow path 24. Between the supply pump 50 and the subtank 22, a branch flow path 25 branches off from the middle of the main flow path 24, and the branch flow path 25 is connected to the recording head 13 via a head filter 28. In addition, a circulation flow path 51 for circulating and returning the ink to the supply source is connected to the recording head 13, and the circulation flow path 51 is connected to the supply pump 50.

[0052] Furthermore, a fifth opening / closing member 52 for opening and closing the main flow path 24 is provided midway along the main flow path 24 between the supply pump 50 and the branch flow path 25, and a sixth opening / closing member 53 for opening and closing the circulation flow path 51 is provided in the circulation flow path 51. The fifth opening / closing member 52 and the sixth opening / closing member 53 are each controlled by the control unit 16 to open or close.

[0053] Next, an example of the operation of the ink supply mechanism 20 of the first modified example will be described.

[0054] In the ink supply mechanism 20, under normal circumstances, the fifth opening / closing member 52 and the sixth opening / closing member 53 are all open. This allows the head pressure of the ink stored in the subtank 22 to act on the recording head 13 via the main flow path 24 and the branch flow path 25, and the ink filled in the supply pump 50 can be appropriately supplied to the recording head 13.

[0055] During ink filling, the ink supply mechanism 20 closes both the fifth opening / closing member 52 and the sixth opening / closing member 53. This allows ink to be filled into the supply pump 50 from the main flow path 24 between the ink container 14 and the supply pump 50.

[0056] During circulation, the ink supply mechanism 20 opens the sixth opening / closing member 53 and closes the fifth opening / closing member 52. This allows the ink to be circulated from the recording head 13 to the supply pump 50 via the circulation flow path 51.

[0057] 5, in a second modified example, the ink supply mechanism 20 may be configured to include only a suction pump 60 that sucks ink from the ink container 14, without including a supply pump 23 that supplies filled ink to the recording head 13. In the second modified example, a suction pump 60 such as a diaphragm pump is provided in the main flow path 24. A branch flow path 25 branches off from the main flow path 24 between the suction pump 60 and the subtank 22, and the branch flow path 25 is connected to the recording head 13 via a head filter 28.

[0058] Furthermore, a seventh opening / closing member 61 for opening and closing the main flow path 24 is provided in the middle of the main flow path 24, between the sub-tank 22 and the branch flow path 25. The seventh opening / closing member 61 is controlled by the control unit 16 to open or close.

[0059] Next, an example of the operation of the ink supply mechanism 20 of the second modified example will be described.

[0060] The ink supply mechanism 20 normally opens the seventh opening / closing member 61. This allows the head pressure of the ink stored in the subtank 22 to act on the recording head 13 via the main flow path 24 and the branch flow path 25, and operates the suction pump 60, thereby supplying ink to the recording head 13.

[0061] During the purging process, the ink supply mechanism 20 closes the seventh opening / closing member 61. This allows the suction pump 60 to operate and supply ink to the recording head 13 without affecting the ink on the subtank 22, thereby performing the purging process.

[0062] In this embodiment, the configuration of the present invention is applied to a printer 1 as an image forming apparatus. However, in other different embodiments, the configuration of the present invention can also be applied to other different image forming apparatuses such as copiers, facsimiles, multifunction machines, etc., so long as they are equipped with an inkjet type ink supply mechanism. [Explanation of symbols]

[0063] 1. Printer (image forming device) 13 Recording head 13, 13K, 13C, 13M, 13Y recording head 14, 14K, 14C, 14M, 14Y ink container 20 Ink supply mechanism 21, 60 Suction pump 22 Subtank 23, 50 Supply pump 24 Main channel 25 Branch Channel 27 Restriction Members 36 Tank body 37 Level Sensor 38 Float 39 Moving parts 40 Float detector

Claims

1. an ink container for storing ink; a sub-tank for storing the ink supplied from the ink container; a main flow path extending downward from the sub-tank and allowing the ink to flow between the ink container and the sub-tank; an ink supply mechanism comprising: a branch flow path that branches off from the middle of the main flow path and receives a head pressure of the ink stored in the sub-tank in order to supply the ink to a recording head.

2. a level sensor for detecting a liquid level of the ink stored in the subtank, The ink supply mechanism according to claim 1, characterized in that the level sensor is composed of a movable sensor having a float floating on the liquid surface at a distance from the inner wall surface of the subtank and a movable part disposed in a position not in contact with the ink and movable to move the float, or a fixed sensor consisting of a capacitance sensor, a photointerrupter or an electrode-type level sensor disposed in a position not in contact with the ink.

3. a pump for supplying the ink from the ink container through the main flow path; 2. The ink supply mechanism according to claim 1, wherein the branch flow path is disposed between the sub-tank and the pump.

4. 2. The ink supply mechanism according to claim 1, further comprising a restricting member that restricts the exchange of the ink between the subtank and the branch channel without changing the head pressure.

5. 5. An image forming apparatus comprising the ink supply mechanism according to claim 1.

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